The invention relates generally to a process of producing residual compressive stress in the surface of a metal workpiece to increase its fatigue strength, and more particularly to a method of producing a residual compressive stress in the external surface of a metal workpiece by forcing the workpiece onto a mandrel to induce a tensile stress in the workpiece and thereafter inducing a compressive stress in the surface of the workpiece by shot blast treatment.
A process of compression stressing metals to increase the fatigue strength thereof by shot-peening is described in U.S. Straub Pat. No. 4,034,585, issued July 12, 1977. The process described therein discloses a process for improving the fatigue strength of metal parts by two sequential shot-peening processes.
U.S. Pat. No. 3,073,022 issued Jan. 15, 1963 similarly shows a method for compression stressing a metal workpiece by subjecting the workpiece to a first shot-peening step using large shot directed at high intensity against the workpiece and then subjecting the workpiece to a second shot-peening step using smaller shot and at a lower intensity.
The U.S. Young et al. Pat. No. 2,542,955 issued Feb. 20, 1951 discloses an apparatus for use in supporting a workpiece to be shot-peened, the apparatus including means for rotating the workpiece.
Attention is also directed to U.S. Pat. No. 1,585,989 issued May 25, 1926 which discloses a method for making spinning rings, the method including the steps of forcing the spinning ring onto a circular mandrel to make the ring circular and thereafter grinding the exterior surface of the ring. Attention is further directed to U.S. Pat. No. 3,210,837 issued Oct. 12, 1965.